[PATCH v10 08/12] iio: adc: ad7768-1: add multiple scan types to support 16-bits mode

[Jonathan Santos <Jonathan.Santos@analog.com>]

When the device is configured to decimation x8, only possible in the
sinc5 filter, output data is reduced to 16-bits in order to support
1 MHz of sampling frequency due to clock limitation.

Use multiple scan types feature to enable the driver to switch
scan type at runtime, making it possible to support both 24-bit and
16-bit resolution.

Reviewed-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
---
v10 Changes:
* None.

v9 Changes:
* Addressed indentation issue.

v8 Changes:
* Fixed typo in David's Email.
* Removed TODO comment related to the spi_bpw_to_bytes() function.

v7 Changes:
* Added TODO comment to use spi_bpw_to_bytes() helper function.
* Minor commit description changes.

v6 Changes:
* None.

v5 Changes:
* None.

v4 Changes:
* None.

v3 Changes:
* Decreased storagebits to 16 for AD7768_SCAN_TYPE_HIGH_SPEED
  scan type.

v2 Changes:
* Included the ".shift" value back to scan_type.
* Changed the number of bytes from regmap_read instead of shifting the 
  ADC sample value when the word size is lower (16-bits).
---
 drivers/iio/adc/ad7768-1.c | 74 ++++++++++++++++++++++++++++++++------
 1 file changed, 64 insertions(+), 10 deletions(-)

diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
index 6efecb0e88b6..55913763313d 100644
--- a/drivers/iio/adc/ad7768-1.c
+++ b/drivers/iio/adc/ad7768-1.c
@@ -140,6 +140,15 @@ struct ad7768_clk_configuration {
 	enum ad7768_pwrmode pwrmode;
 };
 
+enum ad7768_scan_type {
+	AD7768_SCAN_TYPE_NORMAL,
+	AD7768_SCAN_TYPE_HIGH_SPEED,
+};
+
+static const int ad7768_mclk_div_rates[] = {
+	16, 8, 4, 2,
+};
+
 static const struct ad7768_clk_configuration ad7768_clk_config[] = {
 	{ AD7768_MCLK_DIV_2, AD7768_DEC_RATE_8, 16,  AD7768_FAST_MODE },
 	{ AD7768_MCLK_DIV_2, AD7768_DEC_RATE_16, 32,  AD7768_FAST_MODE },
@@ -154,6 +163,22 @@ static const struct ad7768_clk_configuration ad7768_clk_config[] = {
 	{ AD7768_MCLK_DIV_16, AD7768_DEC_RATE_1024, 16384, AD7768_ECO_MODE },
 };
 
+static const struct iio_scan_type ad7768_scan_type[] = {
+	[AD7768_SCAN_TYPE_NORMAL] = {
+		.sign = 's',
+		.realbits = 24,
+		.storagebits = 32,
+		.shift = 8,
+		.endianness = IIO_BE,
+	},
+	[AD7768_SCAN_TYPE_HIGH_SPEED] = {
+		.sign = 's',
+		.realbits = 16,
+		.storagebits = 16,
+		.endianness = IIO_BE,
+	},
+};
+
 static const struct iio_chan_spec ad7768_channels[] = {
 	{
 		.type = IIO_VOLTAGE,
@@ -163,13 +188,9 @@ static const struct iio_chan_spec ad7768_channels[] = {
 		.indexed = 1,
 		.channel = 0,
 		.scan_index = 0,
-		.scan_type = {
-			.sign = 's',
-			.realbits = 24,
-			.storagebits = 32,
-			.shift = 8,
-			.endianness = IIO_BE,
-		},
+		.has_ext_scan_type = 1,
+		.ext_scan_type = ad7768_scan_type,
+		.num_ext_scan_type = ARRAY_SIZE(ad7768_scan_type),
 	},
 };
 
@@ -182,6 +203,7 @@ struct ad7768_state {
 	unsigned int vcm_output_sel;
 	struct clk *mclk;
 	unsigned int mclk_freq;
+	unsigned int dec_rate;
 	unsigned int samp_freq;
 	struct completion completion;
 	struct iio_trigger *trig;
@@ -319,6 +341,15 @@ static int ad7768_scan_direct(struct iio_dev *indio_dev)
 	if (ret)
 		return ret;
 
+	/*
+	 * When the decimation rate is set to x8, the ADC data precision is
+	 * reduced from 24 bits to 16 bits. Since the AD7768_REG_ADC_DATA
+	 * register provides 24-bit data, the precision is reduced by
+	 * right-shifting the read value by 8 bits.
+	 */
+	if (st->dec_rate == 8)
+		readval >>= 8;
+
 	/*
 	 * Any SPI configuration of the AD7768-1 can only be
 	 * performed in continuous conversion mode.
@@ -532,6 +563,8 @@ static int ad7768_set_freq(struct ad7768_state *st,
 	if (ret < 0)
 		return ret;
 
+	st->dec_rate = ad7768_clk_config[idx].clk_div /
+		       ad7768_mclk_div_rates[ad7768_clk_config[idx].mclk_div];
 	st->samp_freq = DIV_ROUND_CLOSEST(st->mclk_freq,
 					  ad7768_clk_config[idx].clk_div);
 
@@ -565,8 +598,13 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
 			   int *val, int *val2, long info)
 {
 	struct ad7768_state *st = iio_priv(indio_dev);
+	const struct iio_scan_type *scan_type;
 	int scale_uv, ret;
 
+	scan_type = iio_get_current_scan_type(indio_dev, chan);
+	if (IS_ERR(scan_type))
+		return PTR_ERR(scan_type);
+
 	switch (info) {
 	case IIO_CHAN_INFO_RAW:
 		if (!iio_device_claim_direct(indio_dev))
@@ -577,7 +615,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
 		iio_device_release_direct(indio_dev);
 		if (ret < 0)
 			return ret;
-		*val = sign_extend32(ret, chan->scan_type.realbits - 1);
+		*val = sign_extend32(ret, scan_type->realbits - 1);
 
 		return IIO_VAL_INT;
 
@@ -587,7 +625,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
 			return scale_uv;
 
 		*val = (scale_uv * 2) / 1000;
-		*val2 = chan->scan_type.realbits;
+		*val2 = scan_type->realbits;
 
 		return IIO_VAL_FRACTIONAL_LOG2;
 
@@ -631,11 +669,21 @@ static const struct attribute_group ad7768_group = {
 	.attrs = ad7768_attributes,
 };
 
+static int ad7768_get_current_scan_type(const struct iio_dev *indio_dev,
+					const struct iio_chan_spec *chan)
+{
+	struct ad7768_state *st = iio_priv(indio_dev);
+
+	return st->dec_rate == 8 ?
+	       AD7768_SCAN_TYPE_HIGH_SPEED : AD7768_SCAN_TYPE_NORMAL;
+}
+
 static const struct iio_info ad7768_info = {
 	.attrs = &ad7768_group,
 	.read_raw = &ad7768_read_raw,
 	.write_raw = &ad7768_write_raw,
 	.read_label = ad7768_read_label,
+	.get_current_scan_type = &ad7768_get_current_scan_type,
 	.debugfs_reg_access = &ad7768_reg_access,
 };
 
@@ -690,9 +738,15 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct ad7768_state *st = iio_priv(indio_dev);
+	const struct iio_scan_type *scan_type;
 	int ret;
 
-	ret = spi_read(st->spi, &st->data.scan.chan, 3);
+	scan_type = iio_get_current_scan_type(indio_dev, &indio_dev->channels[0]);
+	if (IS_ERR(scan_type))
+		goto out;
+
+	ret = spi_read(st->spi, &st->data.scan.chan,
+		       BITS_TO_BYTES(scan_type->realbits));
 	if (ret < 0)
 		goto out;
 
-- 
2.34.1